This invention relates to a media feed assembly for a label/tag printer or other media manipulating device for loading, holding, advancing, and retracting media in the device.
Inkjet printers typically include a media advancing assembly and a print head that repeatedly moves in a path that is transverse to the direction of the advancing media. After every pass of the print head, the media advances a distance equal to the width of a print swath. The direction and amount of media travel is typically controlled by a processor that sends signals to a drive mechanism associated with a media feed roller. In response to control signals from the processor, the feed roller is caused to rotate a predetermined amount and, together with a set of pinch rollers, pinch and feed the media an amount desired for printing, cutting, and/or other operations. The print head typically has an array of four nozzles, with each nozzle representing a different color to be applied to the media, e.g. cyan, magenta, yellow, and black. In order to obtain millions of colors, two or more of the nozzles may be directed to deposit ink at the same location on the media or the nozzles may be directed to deposit ink at a precise location with respect to deposits from other nozzles. Hence, the accuracy of media advancement is of prime importance to the quality of the resulting print. Under-advancement of the media will cause the print swaths to overlap, while over-advancement of the media will cause the print swaths to be separated.
The accuracy of media advancement is affected by slippage that can occur between the media and the feed roller. In order to prevent slippage, good traction between the media and feed roller is necessary. Good traction is dependent on many factors, such as the pinch pressure exerted by the pinch rollers on the feed roller, the coefficient of friction between the media and the feed roller, the acceleration of the feed roller, as well as forward and rearward tension forces acting on the media.
In the on-demand label/tag printing industry, the printing media is normally either in the form of a continuous roll or a continuous folded stack of labels/tags. Prior to printing, the media from the roll or stack is typically fed through the printer until a forward edge of the media exits the feed roller at a position under the print head. In most instances, the pinch rollers must be released from the feed roller to ensure that the media can be loaded without obstruction. Once the media is loaded, the pinch rollers are lowered to thereby xe2x80x9cpinchxe2x80x9d or compress the media against the feed roller.
Many printers have an elaborate feed path with one or more turns that are prone to loading or feeding errors, such as buckling and jamming of the media, as it is fed through the printer. In addition, one or more turns in the feed path may cause delamination of die-cut labels from their backing sheets, especially when the label is on the outside of a turn. In addition, air pockets between the label and backing sheet can occur as the media curvature changes direction during travel along the feed path.
Although these problems are substantially reduced or eliminated with the provision of a generally linear or straight-line feed path between the continuous roll or folded stack and the feed roller, several other problems may arise. In particular, when adhesive label media with a backing sheet are used, slippage between the feed roller and the label media can occur since the coefficient of friction between the relatively slick backing sheet and the feed roller is comparatively less than the coefficient of friction between plain paper media and the feed roller. In order to prevent slippage, a much higher pinch pressure on the adhesive label is needed than on the plain paper media. However, the higher pinch pressure can deform the media as well as the feed roller, which is typically constructed of rubber, and reduce the effective diameter of the feed roller. Consequently, the media tends to be under-advanced which in turn causes the print swaths to overlap.
Continuous media in an inkjet printer is often subject to tension in the forward and backward directions with respect to the feed roller. Backward tensioning may occur when media is pulled from a supply roll, while forward tensioning may occur when the printed media is wrapped over an edge to dispense the die cut label. Media tensioning, whether forward or backward, can reduce the grip between the media and the drive roller and lead to slippage. Hence, higher pinch pressures are necessary to counteract the negative tensioning effects. Again, the higher pinch pressures can deform the media and the feed roller, leading to overlapping print swaths.
A further problem arises when the media is subjected to a series of discontinuous start/stop cycles during printing. As the feed roller rotates through cycles of high acceleration and deceleration for every print swath, the sudden pull of the media at the beginning of a cycle together with the back tension on the media results in media slippage if the pinch pressure is insufficient. This is even more pronounced with higher throughput requirements of inkjet printers designed for the high speed label printing industry when compared to inkjet printers designed for home or office use. Consequently, a relatively high pinch pressure is needed to reduce slippage and ensure accuracy of the media position during printing.
Media skewing is also a problem associated with inkjet printers since there is typically only a single line of contact between the media and the feed roller and pinch rollers. Media skewing is largely dependent on the parallelism between the feed roller and pinch rollers. When the feed roller and pinch rollers are not parallel, the line of contact between the feed roller and pinch rollers will be skewed, resulting in media skewing as well. In order to ensure parallel alignment between the feed roller and pinch rollers, relatively tight tolerances in the related parts are required.
According to the invention, an assembly for feeding media associated with a printer or other media manipulating device is provided. The assembly comprises a media feed roller adapted for rotational movement about a feed roller axis, a first roller support member with a first pinch roller mounted for rotational movement about a first pinch roller axis, and a second roller support member with a second pinch roller mounted for rotational movement about a second pinch roller axis. The first and second pinch rollers are positionable for applying pressure to the feed roller at first and second pinch locations, respectively. One of the roller support members is movable with respect to the other of the roller support members to thereby vary the distance between the first and second pinch locations.